1. Field of the Invention:
The invention relates to an electrical power transmission device having phase conductors which carry alternating current and have a transmission impedance, and having casing conductors which are inductively coupled to the phase conductors, with a first end and a second end of each casing conductor together with a reactance forming a casing circuit, and with an electronic assembly being provided in order to vary the impedance of the casing circuit.
Cables or gas-insulated lines (GIL) are used for power distribution purposes, in order to transmit large amounts of energy between different grid systems. GILs comprise phase conductors which extend in tubular and gas-insulated casing conductors, and, because of their low transmission impedance, offer the capability to transmit power levels of several thousand megawatts with low losses. However, despite this low transmission impedance, the distribution of high-power currents between grid systems may be adversely affected, for example, when such GILs are integrated.
DE 199 37 661 A1 discloses a circuit arrangement of the generic type for a three-phase transmission system in which a casing conductor is provided for each phase conductor. A capacitive reactance is connected in series with the casing conductor and is used to compensate for the series impedance of the phase conductor. Compensation such as this reduces or minimizes the wattless component in the transmission system.
Furthermore, DE 199 37 661 A1 proposes that a plurality of capacitors be connected or disconnected as a function of the load on the transmission system. This circuit arrangement has the disadvantage that the impedance can only be reduced for power-factor correction.